[Intel-gfx] [PATCH] drm/i915: Drop stealing of bits from i915_sw_fence function pointer

Tvrtko Ursulin tvrtko.ursulin at linux.intel.com
Wed Sep 22 15:25:04 UTC 2021


On 22/09/2021 16:21, Tvrtko Ursulin wrote:
> 
> On 22/09/2021 15:57, Matthew Brost wrote:
>> Rather than stealing bits from i915_sw_fence function pointer use
>> seperate fields for function pointer and flags. If using two different
>> fields, the 4 byte alignment for the i915_sw_fence function pointer can
>> also be dropped.
>>
>> v2:
>>   (CI)
>>    - Set new function field rather than flags in __i915_sw_fence_init
>>
>> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/intel_display.c  |  2 +-
>>   drivers/gpu/drm/i915/gem/i915_gem_context.c   |  2 +-
>>   drivers/gpu/drm/i915/i915_request.c           |  4 ++--
>>   drivers/gpu/drm/i915/i915_sw_fence.c          | 12 +++++------
>>   drivers/gpu/drm/i915/i915_sw_fence.h          | 21 +++++++++----------
>>   drivers/gpu/drm/i915/i915_sw_fence_work.c     |  2 +-
>>   .../gpu/drm/i915/selftests/i915_sw_fence.c    |  2 +-
>>   drivers/gpu/drm/i915/selftests/lib_sw_fence.c |  4 ++--
>>   8 files changed, 23 insertions(+), 26 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c 
>> b/drivers/gpu/drm/i915/display/intel_display.c
>> index a7ca38613f89..6d5bb55ffc82 100644
>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>> @@ -10323,7 +10323,7 @@ static void intel_atomic_commit_work(struct 
>> work_struct *work)
>>       intel_atomic_commit_tail(state);
>>   }
>> -static int __i915_sw_fence_call
>> +static int
>>   intel_atomic_commit_ready(struct i915_sw_fence *fence,
>>                 enum i915_sw_fence_notify notify)
>>   {
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c 
>> b/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> index c2ab0e22db0a..df5fec5c3da8 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> @@ -800,7 +800,7 @@ static void free_engines_rcu(struct rcu_head *rcu)
>>       free_engines(engines);
>>   }
>> -static int __i915_sw_fence_call
>> +static int
>>   engines_notify(struct i915_sw_fence *fence, enum 
>> i915_sw_fence_notify state)
>>   {
>>       struct i915_gem_engines *engines =
>> diff --git a/drivers/gpu/drm/i915/i915_request.c 
>> b/drivers/gpu/drm/i915/i915_request.c
>> index ce446716d092..945d3025a0b6 100644
>> --- a/drivers/gpu/drm/i915/i915_request.c
>> +++ b/drivers/gpu/drm/i915/i915_request.c
>> @@ -719,7 +719,7 @@ void i915_request_cancel(struct i915_request *rq, 
>> int error)
>>       intel_context_cancel_request(rq->context, rq);
>>   }
>> -static int __i915_sw_fence_call
>> +static int
>>   submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify 
>> state)
>>   {
>>       struct i915_request *request =
>> @@ -755,7 +755,7 @@ submit_notify(struct i915_sw_fence *fence, enum 
>> i915_sw_fence_notify state)
>>       return NOTIFY_DONE;
>>   }
>> -static int __i915_sw_fence_call
>> +static int
>>   semaphore_notify(struct i915_sw_fence *fence, enum 
>> i915_sw_fence_notify state)
>>   {
>>       struct i915_request *rq = container_of(fence, typeof(*rq), 
>> semaphore);
>> diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c 
>> b/drivers/gpu/drm/i915/i915_sw_fence.c
>> index c589a681da77..1c080dd1f718 100644
>> --- a/drivers/gpu/drm/i915/i915_sw_fence.c
>> +++ b/drivers/gpu/drm/i915/i915_sw_fence.c
>> @@ -34,7 +34,7 @@ enum {
>>   static void *i915_sw_fence_debug_hint(void *addr)
>>   {
>> -    return (void *)(((struct i915_sw_fence *)addr)->flags & 
>> I915_SW_FENCE_MASK);
>> +    return (void *)(((struct i915_sw_fence *)addr)->fn);
>>   }
>>   #ifdef CONFIG_DRM_I915_SW_FENCE_DEBUG_OBJECTS
>> @@ -126,10 +126,7 @@ static inline void debug_fence_assert(struct 
>> i915_sw_fence *fence)
>>   static int __i915_sw_fence_notify(struct i915_sw_fence *fence,
>>                     enum i915_sw_fence_notify state)
>>   {
>> -    i915_sw_fence_notify_t fn;
>> -
>> -    fn = (i915_sw_fence_notify_t)(fence->flags & I915_SW_FENCE_MASK);
>> -    return fn(fence, state);
>> +    return fence->fn(fence, state);
>>   }
>>   #ifdef CONFIG_DRM_I915_SW_FENCE_DEBUG_OBJECTS
>> @@ -242,10 +239,11 @@ void __i915_sw_fence_init(struct i915_sw_fence 
>> *fence,
>>                 const char *name,
>>                 struct lock_class_key *key)
>>   {
>> -    BUG_ON(!fn || (unsigned long)fn & ~I915_SW_FENCE_MASK);
>> +    BUG_ON(!fn);
>>       __init_waitqueue_head(&fence->wait, name, key);
>> -    fence->flags = (unsigned long)fn;
>> +    fence->fn = fn;
>> +    fence->flags = 0;
>>       i915_sw_fence_reinit(fence);
>>   }
>> diff --git a/drivers/gpu/drm/i915/i915_sw_fence.h 
>> b/drivers/gpu/drm/i915/i915_sw_fence.h
>> index 30a863353ee6..70ba1789aa89 100644
>> --- a/drivers/gpu/drm/i915/i915_sw_fence.h
>> +++ b/drivers/gpu/drm/i915/i915_sw_fence.h
>> @@ -17,26 +17,25 @@
>>   struct completion;
>>   struct dma_resv;
>> +struct i915_sw_fence;
>> +
>> +enum i915_sw_fence_notify {
>> +    FENCE_COMPLETE,
>> +    FENCE_FREE
>> +};
>> +
>> +typedef int (*i915_sw_fence_notify_t)(struct i915_sw_fence *,
>> +                      enum i915_sw_fence_notify state);
>>   struct i915_sw_fence {
>>       wait_queue_head_t wait;
>> +    i915_sw_fence_notify_t fn;
>>       unsigned long flags;
> 
> Looks good to me. I'd just make the flags narrower now that they can be, 
> and put them down..
> 
>>       atomic_t pending;
> 
> .. here as unsigned int and so we save 4 bytes, maybe.

No this won't work due test_and_set_bit needs a long, oh well.

> 
> In fact, unless CONFIG_DRM_I915_SW_FENCE_CHECK_DAG is on, which it won't 
> be on release builds, I don't think anything uses flags any more. So you 
> could even omit the flags in that case. Might be cumbersome so can leave 
> for later, but would sure be nice not to waste space if we can avoid it.
> 
> Also please double check if i915_sw_fence_reinit() will be fine and 
> won't bug on since fence->flags is always zero now I think.

But these two are worth checking out.

Regards,

Tvrtko

> 
> Regards,
> 
> Tvrtko
> 
>>       int error;
>>   };
>>   #define I915_SW_FENCE_CHECKED_BIT    0 /* used internally for DAG 
>> checking */
>> -#define I915_SW_FENCE_PRIVATE_BIT    1 /* available for use by owner */
>> -#define I915_SW_FENCE_MASK        (~3)
>> -
>> -enum i915_sw_fence_notify {
>> -    FENCE_COMPLETE,
>> -    FENCE_FREE
>> -};
>> -
>> -typedef int (*i915_sw_fence_notify_t)(struct i915_sw_fence *,
>> -                      enum i915_sw_fence_notify state);
>> -#define __i915_sw_fence_call __aligned(4)
>>   void __i915_sw_fence_init(struct i915_sw_fence *fence,
>>                 i915_sw_fence_notify_t fn,
>> diff --git a/drivers/gpu/drm/i915/i915_sw_fence_work.c 
>> b/drivers/gpu/drm/i915/i915_sw_fence_work.c
>> index 5b33ef23d54c..d2e56b387993 100644
>> --- a/drivers/gpu/drm/i915/i915_sw_fence_work.c
>> +++ b/drivers/gpu/drm/i915/i915_sw_fence_work.c
>> @@ -23,7 +23,7 @@ static void fence_work(struct work_struct *work)
>>       dma_fence_put(&f->dma);
>>   }
>> -static int __i915_sw_fence_call
>> +static int
>>   fence_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify 
>> state)
>>   {
>>       struct dma_fence_work *f = container_of(fence, typeof(*f), chain);
>> diff --git a/drivers/gpu/drm/i915/selftests/i915_sw_fence.c 
>> b/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
>> index cbf45d85cbff..daa985e5a19b 100644
>> --- a/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
>> +++ b/drivers/gpu/drm/i915/selftests/i915_sw_fence.c
>> @@ -28,7 +28,7 @@
>>   #include "../i915_selftest.h"
>> -static int __i915_sw_fence_call
>> +static int
>>   fence_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify 
>> state)
>>   {
>>       switch (state) {
>> diff --git a/drivers/gpu/drm/i915/selftests/lib_sw_fence.c 
>> b/drivers/gpu/drm/i915/selftests/lib_sw_fence.c
>> index 080b90b63d16..eb59a41bdb79 100644
>> --- a/drivers/gpu/drm/i915/selftests/lib_sw_fence.c
>> +++ b/drivers/gpu/drm/i915/selftests/lib_sw_fence.c
>> @@ -26,7 +26,7 @@
>>   /* Small library of different fence types useful for writing tests */
>> -static int __i915_sw_fence_call
>> +static int
>>   nop_fence_notify(struct i915_sw_fence *fence, enum 
>> i915_sw_fence_notify state)
>>   {
>>       return NOTIFY_DONE;
>> @@ -89,7 +89,7 @@ struct heap_fence {
>>       };
>>   };
>> -static int __i915_sw_fence_call
>> +static int
>>   heap_fence_notify(struct i915_sw_fence *fence, enum 
>> i915_sw_fence_notify state)
>>   {
>>       struct heap_fence *h = container_of(fence, typeof(*h), fence);
>>


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